This invention generally relates to a work piece positioning device and more particularly, to a highly accurate work piece positioning device which is used in conjunction with and controlled by an automated system or device such as a robotic welder.
Robotic welders have been used in conjunction with work piece positioning devices which are driven to predetermined desired positions by two drive systems, one of which controls the rotation of the work piece about the x axis and the other of which controls rotation about the y axis. Heretofore, these drive systems have utilized spur gears to produce desired rotation. However, spur gears are relatively inaccurate due to the backlash which is inherent in a spur gear system. Since accuracy is an important requirement of a satisfactory positioning device, various expedients for reducing the backlash in spur gear systems have been utilized.
One such expedient involves joining two identical spur gears side-by-side with one gear rotated slightly with respect to the other so that the gear teeth do not line up perfectly. The resulting modified spur gear is then used with an unmodified spur gear with one of the two being driven by the other. This provides a combination which is initially more accurate than two unmodified spur gears in combination. However, this initial improvement in accuracy is not permanent due to increased or excessive wear. Other drives based on spur gears have been proposed but they also have been subJect to excessive wear.
Further, spur gear systems are limited to relatively low gear ratios which inherently are less accurate than gear systems having higher gear ratios in respect to drive motor error.
The object of this invention generally stated is the provision of a work piece positioning device which is particularly useful for accurately positioning work pieces such as work pieces to be welded in predetermined positions or attitudes.
An important object of the invention is the provision of such work piece positioning devices or machines which are adapted to be controlled by a robot for repetitive operation in commercial production.
A further object of the invention is the provision of such a work piece positioning device which incorporates one sub-assembly which is rotatable about an x axis and a second sub-assembly carried by the first sub-assembly which is rotatable about a y axis, with each of the sub-assemblies being independently and separately controlled by separate or independent electric motors which in turn can be controlled by a suitably interconnected and programmed robot.
A further important object of the invention is the provision of such a work piece positioning device wherein the tiltable or rotatable sub-assemblies are rotated or tilted by the action of a worm and worm gear.
Another important object of the invention is the provision of such a work piece positioning device wherein the worm and worm gear drive combinations are adapted to be locked in a desired or predetermined condition by increasing the force between the worm and worm gear in excess of that used for driving movement.
Certain other objects of the invention will be obvious and others will be apparent to those skilled in the art from the following detailed description of a presently preferred embodiment of the invention taken in connection with the accompanying drawings wherein: